In other words, it can be said that the present invention relates mainly to the type of petroleum wells which may be termed an oil producer, such oil producer producing mainly oil and some gas. This is different from petroleum wells (reservoirs) which are termed gas producer's, which gas producers often also produce some liquid, for example in the form of condensate and water. By such a liquid production (in a gas well) and low pressure in the reservoir, such a well could, however, gradually “drown”, and the need for gas lift may be required. Thus, the present invention also relates to gas lift for gas wells.
Most petroleum producers (wells) will have a characterisation somewhat between these extremes (liquid with some gas-gas with some liquid), the liquid parts here being considered as having reasonably low viscosity.
When an oil producer (with some gas included) gradually looses its productivity by falling reservoir pressure (and lowest practical receiving pressure above ground), the pressure head in the production tubing will gradually balance the reservoir pressure. Production will then stop and the liquid level in the well will gradually come to rest below ground level.
Gas which is still released from the oil production tubing and in the zone close to the perforation, will bubble up through the production string, and then without effectively contributing to the reduction of pressure head.
It is in connection with this type of wells that the present invention has been developed.
By such oil producing wells also the residual gas will gradually be terminated, and in order to prevent such wells from “dying” it is common to introduce gas lift to reduce the pressure head resistance.
However, the present invention is to the fact of utilising the previously ineffective gas bubbles flowing through or bubbling past the liquid in a production tubing string, and then in surprising and new manner.